iscsi-target: return -ENOMEM instead of -1 in case of failed kmalloc()

Smatch complains about returning hard coded error codes, silence this
warning.

drivers/target/iscsi/iscsi_target_parameters.c:211
   iscsi_create_default_params() warn: returning -1 instead of -ENOMEM is sloppy

Signed-off-by: Luis de Bethencourt <luisbg@osg.samsung.com>
Reviewed-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>